MODAPS PCR VNP 20-011
| PCR Number | VNP 20-011 |
|---|---|
| Date | 2020-12-23 |
| Initiator | Guoqing (Gary) Lin |
| Abstract | PGE501/Geolocation 3.0.31 in VNP_1Vam7 3.0.25 and VJ1_1Vam7 2.1.4. PGE560/Control Point v2.0.4 in VNP_1bm7 3.0.35 and VJ1_1bm7 2.1.7. PGE599 1.0.9 For VIGMU, the mag matrix as switched sign and the u_aft vector is flipped within the code. This also requires changing the alpha, beta, and gammaa angles within the LUT to accommodate the change.For the time-dependant attitude corrections, 3 new variables were added to the LUTs: a count, an array of times, and an array of roll/pitch/yaw correction angles. The arrays of times and corrections were assigned to be 1000 long, and the count variable tells the code which elements of the arrays are valid. This method allows the LUT to not change format/size while allowing essentially more elements to be added to the arrays. Currently only about 50 elements are used, so it is unlikely that more elements will be necessary when considering the lifetime of the mission. For the eaGap flagging, the existing 2-bits of the scan quality flag field are put to use. Previously, the flagging did not work, and now it can flag if the data has no gaps, "small" gaps, "medium" gaps, and "large" gaps. The sizes are defined as follows: No gap: 0 < gap <= 1.5sec (interpolation), Small gap: 1.5sec < gap <= 9sec (interpolation), Medium gap: 1.5sec < edge of granule gap <= 9sec (extrapolation), Large gap: 9sec < gap (no geolocation produced). Note that the nominal data rate is 1Hz (1sec between SCdiary entries) |
| Problem Statement | Geolocation process revised for use in the C2 reprocessing of VIIRS (C2 for SNPP and C2.1 for JPSS1). New Version is PGE501 3.0.31, which is found in VNP_1Vam7 3.0.25 and VJ1_1Vam7 2.1.4. PGE560/Control Point v2.0.4 in VNP_1bm7 3.0.35 and VJ1_1bm7 2.1.7 code revised to make use of new set of CHIP files |
| Description of Change | 1) VIIRS Instrument Geometric Model Update (VIGMU), 2) time-dependant attitude corrections to the inst2sc rotation matrix, and 3) improved flagging of ephemeris and attitude data gaps (eaGaps) within the input data. The VIGMU change corrects the sign of the magnification matrix to eliminate wobble in the output. The time-dependant attitude corrections provide observation based corrections to the mounting matrix that are especially useful for reprocessing - additionally used to fix the VIGMU parameters for the other scan control electronics (SCE) side and to correct for geolocation error of about 800 m for about 7 hours due to en error in on-orbit operations. Control Point: changes are to make use of new CHIP files and to resolve a bug introduced that was causing certain datafields to be populated with all 0 values. |
| Products Affected | VNP03MOD, VNP03IMG, VNP03DNB, VJ103MOD, VJ103IMG, VJ103DNB, VNPGCP, VJ1GCP |
| Software Affected | PGE501 3.0.31; PGE599 1.0.9; PGE560 2.0.4 Process: NPP_PR03 |
| Processing String to Receive the Change | S-NPP Forward Processing. S-NPP Reprocessing. J1 Forward Processing. J1 Reprocessing. |
| Downstream Product Effects | All VIIRS land products |
| Data Granules to be Used for Science Testing | Several science tests of L1 and downstream land product suite generating global products from 16-day period ran at Land SIPS |
| Justification | The VIGMU change corrects previously incorrect parameters in the LUT, the time-dependant attitude correction enables improved accuracy of results, and the eaGap flagging is to improve downstream handling of data issues. |
| Effective Date for Implementation of Change | Completed |
| Status | Major algorithm development completed. Guoqing (Gary) Lin approved 10/28/2020. Sadashiva Devadiga approved 10/28/2020 (SNPP), 01/08/2021 (J1). Gang Ye approved on 01/09/2021. |
